diff --git a/client/register.go b/client/register.go
index 2f8885e..79da6de 100644
--- a/client/register.go
+++ b/client/register.go
@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"path"
+	"strconv"
 	"time"
 )
 
@@ -20,7 +21,7 @@ Register will cache the key in the file system and keep it up to date using the
 -r removes all existing registered keys. -k or -f will instead replace all registered keys with those specified
 -k specifies a specific key identifier to register
 -f specifies a file containing a new line separated list of key identifiers
--t specifies a timeout for getting the key from the daemon in seconds
+-t specifies a timeout for getting the key from the daemon (e.g. '5s', '500ms')
 -g gets the key as well
 
 For a machine to access a certain key, it needs permissions on that key.
@@ -39,11 +40,28 @@ var registerRemove = cmdRegister.Flag.Bool("r", false, "")
 var registerKey = cmdRegister.Flag.String("k", "", "")
 var registerKeyFile = cmdRegister.Flag.String("f", "", "")
 var registerAndGet = cmdRegister.Flag.Bool("g", false, "")
-var registerTimeout = cmdRegister.Flag.Int("t", 5, "")
+var registerTimeout = cmdRegister.Flag.String("t", "5s", "")
 
 const registerRecheckTime = 10 * time.Millisecond
 
+func parseTimeout(val string) (time.Duration, error) {
+	// For backwards-compatibility, a timeout value that is a simple integer will
+	// be treated as a number of seconds. This ensures that the historical usage
+	// of the timeout flag like '-t5' retains the same meaning.
+	if secs, err := strconv.Atoi(val); err == nil {
+		return time.Duration(secs) * time.Second, nil
+	}
+
+	// For all other values, use time.ParseDuration.
+	return time.ParseDuration(val)
+}
+
 func runRegister(cmd *Command, args []string) *ErrorStatus {
+	timeout, err := parseTimeout(*registerTimeout)
+	if err != nil {
+		return &ErrorStatus{fmt.Errorf("Invalid value for timeout flag: %s", err.Error()), false}
+	}
+
 	k := NewKeysFile(path.Join(daemonFolder, daemonToRegister))
 	if *registerRemove && *registerKey == "" && *registerKeyFile == "" {
 		// Short circuit & handle `knox register -r`, which is expected to remove all keys
@@ -66,7 +84,6 @@ func runRegister(cmd *Command, args []string) *ErrorStatus {
 		return &ErrorStatus{fmt.Errorf("You must include a key or key file to register. see 'knox help register'"), false}
 	}
 	// Get the list of keys to add
-	var err error
 	var ks []string
 	if *registerKey == "" {
 		f := NewKeysFile(*registerKeyFile)
@@ -99,13 +116,13 @@ func runRegister(cmd *Command, args []string) *ErrorStatus {
 	// If specified, force retrieval of keys
 	if *registerAndGet {
 		key, err := cli.CacheGetKey(*registerKey)
-		c := time.After(time.Duration(*registerTimeout) * time.Second)
+		c := time.After(timeout)
 		for err != nil {
 			select {
 			case <-c:
 				return &ErrorStatus{fmt.Errorf(
-					"Error getting key from daemon (hit timeout after %d seconds); check knox logs for details (most recent error: %v)",
-					*registerTimeout, err), false}
+					"Error getting key from daemon (hit timeout after %s seconds); check knox logs for details (most recent error: %v)",
+					timeout.String(), err), false}
 			case <-time.After(registerRecheckTime):
 				key, err = cli.CacheGetKey(*registerKey)
 			}
diff --git a/client/register_test.go b/client/register_test.go
new file mode 100644
index 0000000..a9e15c9
--- /dev/null
+++ b/client/register_test.go
@@ -0,0 +1,29 @@
+package client
+
+import (
+	"testing"
+	"time"
+)
+
+func TestParseTimeout(t *testing.T) {
+	testCases := []struct {
+		str string
+		dur time.Duration
+	}{
+		{"5", 5 * time.Second},
+		{"5s", 5 * time.Second},
+		{"0.5s", 500 * time.Millisecond},
+		{"500ms", 500 * time.Millisecond},
+	}
+
+	for _, tc := range testCases {
+		r, err := parseTimeout(tc.str)
+		if err != nil {
+			t.Errorf("error parsing value %s: %s", tc.str, err)
+			continue
+		}
+		if r != tc.dur {
+			t.Errorf("mismatch: %s should parse to %s", tc.str, tc.dur.String())
+		}
+	}
+}